1. Field of Invention
The present invention relates to a multicarrier communication apparatus, an integrated circuit, and a multicarrier communication method, in which communication is performed by using a plurality of carriers.
2. Description of Related Art
A transmission method using a plurality of subcarriers, such as an OFDM (Orthogonal Frequency Division Multiplexing) method, has a major advantage that high quality communication is possible even when the communication is performed through a rough transmission line, and has been used for not only wireless communication but also wired communication such as power line communication.
A multicarrier communication apparatus, which performs such communication using a plurality of subcarriers, transmits bit data, which are to be transmitted, on a transmitting side by converting the bit data to symbol data; performing a symbol mapping according to the symbol data; converting the data to time-axis data via an inverse FFT transform or an inverse wavelet transform; performing a parallel-serial transform; and converting the data to a base-band analog signal via a DA conversion. The multicarrier communication apparatus obtains reception bit data on a receiving side by converting a received signal to a digital signal via an AD conversion; performing a serial-parallel transform; converting the data to frequency-axis data via an FFT transform or a wavelet transform; and performing a demapping.
Such multicarrier communication apparatus has a carrier detection function that determines whether another apparatus is transmitting a signal to a transmission line, and performs a transmission process when another apparatus is not using the transmission line and when a transmission request is received.
Carrier detection of the multicarrier communication apparatus, as shown in Related Art 1 (Japanese Laid-Open Patent Publication 2001-94527), for example, is performed based on an AD converted reception signal. As shown in Related Art 2 (U.S. 20050037722A1), carrier detection may also be performed based on a signal obtained by converting AD converted digital data to frequency-axis data.
In the case where carrier detection is performed based on an AD converted reception signal, correlation of a signal in a time domain is used, and carrier detection can be realized generally by using a simple circuit or by performing a simple data processing process. However, noise which has a correlation in a time waveform can be falsely detected as indicating existence of a carrier. On the other hand, carrier detection based on a signal after being converted to frequency-axis data uses correlation between subcarriers in a frequency domain, and therefore has a high detection accuracy. However, since transform (e.g., FFT, Wavelet Transform) of a received signal from a time domain to a frequency domain is always required, an increase in power consumption is unavoidable.